JPH0810922B2 - Interpolation filter device - Google Patents

Description

TECHNICAL FIELD The present invention relates to an interpolation filter device applied to a time axis corrector or the like.

Conventional technology In VTR slow playback, etc., the field sequence of the playback signal occurs irregularly, so it does not meet the broadcasting standard as it is.

Therefore, the reproduction signal is fitted to the field-continuous signal by using the time axis corrector to correct the field sequence of the reproduction video signal. In such a case, the video signal is often interpolated using the concept of an interpolation filter to reduce the vertical movement of the video during special reproduction.

A fourth conventional example of the best known interpolation filter
Shown in the figure. 1, 2 are input terminals and output terminals for video signals,
3 is a 1H delay line (1H is 1 horizontal scanning period), 4 and 5 are coefficient multipliers,
6 is an adder and 7 is a SW. When the fields of the playback video signal and output video signal are different, connect SW7 to the H side,
Output a signal that is 1/2 of the current signal and 1/2 of the 1H-delayed signal. When the fields of the reproduced video signal and the output video signal match, SW7 is connected to the L side and the current signal Is output as is. However, this filter has only about half the vertical resolution when SW7 is interpolating on the H side as compared with the case where it is not interpolating. Therefore, there is a drawback that flicker occurs due to the difference in resolution when the SW is switched in field units during special reproduction.

As a clever method for eliminating this flicker, there is a second conventional example of an interpolation filter as shown in FIG. (See “The General Design of a Digital Still Storage”)
ills-Storage) System For Use With An Electronic Rostrum Color (System For Use With An
Electronic Rostrum Color) Camera (Camera. ") BBC RD 1980/12) In the figure, the same numbers and operations as in Figure 4 are performed. 41, 42, 43, 44 are the first and second
3rd, 4th and 2nd coefficient multipliers, each having a coefficient value of 1/4, 3/4, 1/4, 3/4 times, and 61 and 62 are first and second adders. Is. When the fields of the reproduced video signal and the output video signal are different, connect SW7 to the H side and output a signal that is 1/4 times the current signal plus 3/4 of the 1H delayed signal When the fields of the output video signal match, SW7 is connected to the L side, and a signal obtained by adding 3/4 times the current signal and 1/4 of the signal delayed by 1H is output. In this method, the flicker phenomenon can be avoided because the filter having the same frequency characteristic is passed through regardless of whether the reproduced video signal and the output video signal are matched.

Problems to be Solved by the Invention The transfer function H (ω) of the second conventional interpolation filter shown in FIG. 5 can be expressed as follows.

When SW7 is on the H side, H1 (ω) = 1/4 + 3 * EXP (−jωT) / 4 (1) When SW7 is on the L side, H2 (ω) = 3/4 + EXP (−jωT) / 4 (( 2) T: 1 horizontal scanning time The squares of the amplitude characteristics in equations (1) and (2) are the same and can be expressed by equation (3).

| H (ω) * H (ω) | = {5/8 + 3 * COS (ωT) / 8} ...
(3) From equation (3), it can be seen that the amplitude characteristic | H (ω) | drops to 1/2 at the angular frequency ω at which ωT = π.

In other words, this interpolation filter was able to avoid the flicker phenomenon, but the vertical resolution was reduced, and VTR operation
When switching from normal playback to special playback, or from special playback to normal playback, there was a problem that the difference in vertical resolution was noticeable in the switching when this interpolation filter was passed or not passed. .

The present invention solves such a conventional problem, and an object of the present invention is to prevent a difference in vertical resolution from occurring depending on whether or not an interpolation filter is inserted.

Means for Solving the Problems An interpolation filter device according to the present invention is a device for correcting irregularity of field continuity of a video signal and creating and outputting an output video signal in a continuous field. And a first coefficient unit for multiplying
/ 4 times a second coefficient unit, a first 1H delay unit that delays the first input signal by 1H, and a third coefficient that makes the output of the first 1H delay unit 3/4 times. And a fourth coefficient unit for multiplying the output of the first 1H delay unit by 1/4, a first adder for adding the outputs of the first and third coefficient units, and the second A second adder for adding the outputs of the fourth coefficient unit, and a second adder for adding the outputs of the first and second adders in accordance with the result of determination as to whether the fields of the video signal and the output video signal are the same. The first filter composed of a switch for switching the output and the second input signal
a fifth coefficient unit for multiplying by α (α is a contour enhancement rate), a second 1H delay unit for delaying the second input signal by 1H, and a 2H delay unit for delaying the second input signal by 2H , The second 1H
A sixth coefficient unit for multiplying the output of the delay unit by 1 + 2α times;
A second filter including a seventh coefficient unit that increases the output of the 2H delay unit by -α times and a third filter that adds the outputs of the fifth to seventh coefficient units, and And the second filter is connected in cascade.

Further, the interpolation filter device of the present invention corrects the irregularity of the field continuity of the video signal, and in the device which creates and outputs the output video signal in continuous fields, the input signal is delayed by 1H, 2H, 3H respectively. The first to third delay devices, the input signal and the outputs of the first to third delay devices, respectively,
/ 4,1 / 4−α / 4,3 / 5 + 5α / 4, −3α / 4 times the first to fourth coefficient units, the input signal and the outputs of the first to third delay units. -3α / 4, 3/4 + 5α / 4, 1 / 4−α / 4, −α /
4th to 5th to 8th coefficient multipliers, 1st adder to add the outputs of the 1st to 4th coefficient multipliers, and 5th to 8th
Output of the first and second adders is switched in accordance with the second adder for adding the outputs of the coefficient multipliers and the determination result of whether the fields of the video signal and the output video signal are the same. And a switch.

Operation The invention of claim 1 of the present application is intended to compensate for the deterioration of the vertical resolution of the above-described conventional interpolation filter by the contour emphasis filter. The transfer function H (ω) of the contour enhancement filter described above can be expressed as in Expression (4).

H (ω) = − α + (1 + 2α) * EXP (−jωT) −α * EXP (−j2ωT) (4) The amplitude characteristic of the formula (4) is as shown in the formula (5).

| H (ω) | = 2 + 2α * {1-COS (ωT)} (5) What can be obtained from the equation (5) is that the amplitude becomes the largest when the angular frequency is such that ωT = π holds, and is almost equal to First of (3)
A filter having an inverse characteristic of the amplitude characteristic of the filter can be configured. As a result, the deterioration of the vertical resolution of the first filter is corrected by the second filter.

Further, the present invention is configured so as to have the same transfer function as the above-mentioned dependent first and second filters, and similarly, has the largest amplitude at each frequency where ωT = π holds, The deterioration of the vertical resolution of the first filter is equivalently corrected by the second filter.

First Embodiment FIG. 1 shows a first embodiment of the interpolation filter device according to the present invention. This example is composed of the second conventional interpolation filter (components 3,41 to 44,61,62 and 7 shown in FIG. 5).
This is the first filter. ) Is followed by a contour enhancement filter (this is referred to as a second filter) in a cascade connection. The same operations as those in FIG. 5 are designated by the same numbers. 31,32 are the second 1H delay line and 2H delay line, 45,4
Reference numerals 6 and 47 denote fifth to seventh coefficient units, respectively, -α, 1 + 2α
And having a coefficient value of -α. Reference numeral 63 is a third adder that adds the outputs of these coefficient units. The output of the same interpolation filter as the conventional example is obtained from SW7 of the first filter, and this output is processed by the second filter 8 and output. The second filter 8 is -α times the current signal and 1 + 2 * of the 1H delayed signal.
The sum of α times and −α times the 2H delay signal is output. The square of the amplitude characteristic | H (ω) | of the first embodiment can be expressed by equation (6).

| H (ω) * H (ω) | = {5/8 + 3 * COS (ωT) / 8} * {1 + 2α * {1-COS (ωT)}} * {1 * 2α * {1-COS (ωT) }} (6) FIG. 2 shows a graph showing the frequency characteristic of the equation (6) with α as a coefficient. What can be obtained from this graph is 0.15 <
When α <0.2, the frequency characteristics are considered to be good over the entire frequency band. However, the same result can be obtained even if the order of the first filter and the second filter shown in FIG. 1 is exchanged.

Next, a second embodiment of the interpolation filter device according to the present invention will be described with reference to FIG. In the figure, those using the same numbers as in FIG. 1 perform the same operation. 33,34,35 are 1H each
Delay line, 2H delay line, 3H delay line, 1 input signal each
It delays H, 2H and 3H. The input signal and the outputs of these delay lines 33 to 35 are given to the first to fourth coefficient units 51 to 54 and the fifth to eighth coefficient units 55 to 58. Coefficient multiplier 51,58
Is -α / 4, coefficient units 52 and 57 are 1 / 4-α / 4, and coefficient units 53 and 56 are 3/4
+ 5α / 4 and coefficient units 54 and 55 are coefficient units having coefficient values of −3α / 4, and the outputs of the coefficient units 51 to 54 and 55 to 58 are given to the first and second adders 61 and 62, respectively. The output is given to the H input terminal and the L input terminal of the switch 7. The second embodiment is a filter having the same transfer function as the first embodiment. That is, the transfer function H (ω) when SW7 is on the H side is obtained by the product of Equation (1) and Equation (4), and H1 (ω) = {1/4 + 3 * EXP (−jωT) / 4 } * {-Α + (1 + 2α) * EXP (-jωT)
−α * EXP (−j2ωT)} = − α / 4 + (1 / 4−α / 4) * EXP (−jωT) + (3/4 + 5α / 4) * EXP (−j2ωT) −3α / 4 * EXP (−j3ωT) (7) Expression (7) is obtained, and the transfer function H (ω) when SW7 is on the L side is the product of Expression (2) and Expression (4). Like

H2 (ω) = {3/4 + * EXP (-jωT) / 4} * {-α + (1 + 2α) * EXP (-jωT)
−α * EXP (−j2ωT)} = − 3α / 4 + (3/4 + 5α / 4) * EXP (−jωT) + (1/4 + α / 4) * EXP (−j2ωT) −α / 4 * EXP (− j3ωT) (8) The operation of the embodiment of FIG. 3 is that the current signal, the 1H delay signal, the 2H delay signal, and the 3H delay signal input to the input terminal 1 pass through the coefficient units 51-54 and adder. It is added at 64 or is input to SW7 which is added at adder 65 through coefficient units 55-58. When the fields of the reproduced video signal and the output video signal are different, SW7 is connected to the H side, and when the fields of the reproduced video signal and the output video signal are the same, SW7 is connected to the L side.

As described above, according to the present invention, the problem of the deterioration of the vertical resolution of the conventional interpolation filter is solved by the contour emphasis filter (second
It is possible to compensate by the VTR operation, and when switching from normal playback to special playback or from special playback to normal playback by the operation of VTR, when switching through the interpolation filter or not. A good image can be obtained with almost no difference in vertical resolution.

[Brief description of drawings]

FIG. 1 is a block diagram showing the first embodiment of the present invention, and FIG.
FIG. 3 is a graph showing the frequency characteristic of the interpolation filter of the present invention, FIG. 3 is a block diagram showing the second embodiment of the present invention,
FIG. 4 is a block diagram showing the first conventional example, and FIG. 5 is a second block diagram.
FIG. 7 is a block diagram showing a conventional example of FIG. 3,31,33 …… 1H delay line, 32,34 …… 2H delay line, 35 …… 3H delay line, 41,42,43,44,45,46,47,51,52,53,54,55 , 56,57,58
…… Coefficient multiplier, 61,62,63,64,65 …… Adder, 7 …… Switch (SW).

Claims (2)

[Claims] 1. A device for correcting irregularity of field continuity of a video signal to create and output an output video signal in continuous fields, wherein a first coefficient for multiplying a first input signal by 1/4. A second coefficient unit for multiplying the first input signal by 3/4, and the first coefficient unit
The first input signal is delayed by 1H (H is the horizontal operation time)
A 1H delay device, a third coefficient device that makes the output of the first 1H delay device 3/4 times, and a fourth coefficient device that makes the output of the first 1H delay device 1/4 times A first adder for adding the outputs of the first and third coefficient multipliers, a second adder for adding the outputs of the second and fourth coefficient multipliers, the video signal and the output video A first filter including a switch that switches the outputs of the first and second adders in accordance with the result of determination whether the field of the signal is the same or not, and the second input signal is multiplied by -α (α is a contour Emphasis rate) 5th
And a second coefficient circuit for delaying the second input signal by 1H.
A 1H delay device, a 2H delay device that delays the second input signal by 2H, a sixth coefficient device that multiplies the output of the second 1H delay device by 1 + 2α, and an output of the 2H delay device is -α. 7th to double
And a second filter including a third adder that adds the outputs of the fifth to seventh coefficient units, and the first filter and the second filter are connected in cascade. An interpolation filter device characterized by: 2. A device for correcting irregularity of field continuity of a video signal and producing and outputting an output video signal in continuous fields, wherein the input signals are 1H (H is horizontal operation time), 2H, 3H, respectively. First to third delay devices for delaying, the input signal and the first to third
The output of the third delay device is -α / 4,1 / 4-α / 4,3 / 4 + 5α, respectively.
/ 4, -3α / 4 times the first to fourth coefficient units, the input signal and the outputs of the first to third delay units are respectively -3α /
4,3 / 4 + 5α / 4,1 / 4−α / 4, −α / 4 times the fifth to eighth coefficient units and the first to fourth output of the first to fourth coefficient units. An adder; a second adder for adding the outputs of the fifth to eighth coefficient multipliers; and the first adder according to a result of determination whether the fields of the video signal and the output video signal are the same. ,
An interpolation filter device comprising a switch for switching the output of the second adder.